We report measurements of the mass density, ΩM, and cosmological-constant energy density, ΩΛ of the universe based on the analysis of 42 type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these supernovae, at redshifts between 0.18 and 0.83, are fitted jointly with a set of supernovae from the Calán/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All supernova peak magnitudes are standardized using a SN Ia light-curve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8ΩM - 0.6ΩΛ ≈ - 0.2 ± 0.1 in the region of interest (ΩM ≲ 1.5). For a flat (ΩM + ΩΛ = 1) cosmology we find ΩflatM = 0.28+0.09-0.08 (1 σ statistical) +0.05-0.04 (identified systematics). The data are strongly inconsistent with a Λ = 0 flat cosmology, the simplest inflationary universe model. An open, Λ = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is nonzero and positive, with a confidence of P(Λ > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is tflat0 = 14.9+1.4-1.1(0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calán/Tololo sample and our high-redshift sample. Excluding those few supernovae that are outliers in color excess or fit residual does not significantly change the results. The conclusions are also robust whether or not a width-luminosity relation is used to standardize the supernova peak magnitudes. We discuss and constrain, where possible, hypothetical alternatives to a cosmological constant.
Publication Source (Journal or Book title)
Perlmutter, S., Aldering, G., Goldhaber, G., Knop, R., Nugent, P., Castro, P., Deustua, S., Fabbro, S., Goobar, A., Groom, D., Hook, I., Kim, A., Kim, M., Lee, J., Nunes, N., Pain, R., Pennypacker, C., Quimby, R., Lidman, C., Ellis, R., Irwin, M., McMahon, R., Ruiz-Lapuente, P., Walton, N., Schaefer, B., Boyle, B., Filippenko, A., Matheson, T., Fruchter, A., Panagia, N., Newberg, H., & Couch, W. (1999). Measurements of Ω and Λ from 42 high-redshift Supernovae. Astrophysical Journal, 517 (2 PART 1), 565-586. https://doi.org/10.1086/307221